Guthrie, U.S. Pat. No. 4,708,757, issued Nov. 24, 1987 to the same inventor as the present application, discloses a method of forming a corrugated panel. In the Guthrie '757 patent, a corrugated panel in which at least the central corrugated sheet is formed from an elastically deformable material such as polyethylene synthetic plastic or spring steel is disposed and secured between a pair of cover sheets. The method of forming the panel includes stretching out a first of the cover sheets and thereafter attaching the ends of the sheet to be corrugated to the first sheet while maintaining the spacing between the remainder of the sheet. This forms a half sinusoidal shape from the sheet to be corrugated. A compressive force is thereafter applied to the sheet to be corrugated which forms it into a number of corrugations having ridges and furrows. The furrows are bonded to the base sheet and a third sheet is positioned on and bonded to the ridges of the corrugated sheet.
Referring to FIGS. 1-6, and particularly to FIG. 1, a panel 10 constructed in accordance with the principles of the Prior Art invention comprises first and second sheets 12, 14 of flexible elastically deformable material preferably a thin sheet of metal such as spring steel or a synthetic plastic such as polyethylene between which a third sheet 16 of similar material is sandwiched. The third sheet 16 is corrugated or wave shaped and is secured to the first and second sheets at respective peaks or ridges of the waves while in a pre-stressed state resulting from the forces applied to the third sheet when forming the corrugated configuration as hereinafter described. The manner of forming the corrugation effects a curvilinear configuration throughout the third sheet, which configuration is substantially sinusoidal.
The panel 10 may be utilized for various purposes such as for packaging, but since the corrugations can be of a large size, the panels have application for wall structures and partitions. Moreover, as illustrated in FIG. 2, especially where the sheets are of synthetic plastic, the voids between the waves of the third sheet and the respective first and second sheets may be filled with an insulating material such as polyurethane foam 18 and the resulting product may be used as insulating wall panels in buildings. Because of the pre-stressed state of the third sheet the panels have substantial strength, but if desired they may be re-enforced to provide a more rigid structure by the addition of stiffeners (not illustrated) between the first and second sheets extending substantially perpendicular to the plane of the waves formed, i.e., substantially parallel to the longitudinal axis of the panel.
The method of forming the panel 10 comprises securing the first sheet 12 substantially at its ends 20, 22 on a flat surface 23 or at least in a stretched disposition so that it forms a substantially planar surface. This may be accomplished by holding the ends by clamping means 24, 26. Thereafter the third sheet 16 is disposed on the first sheet and the ends thereof secured by clamping to the first sheet. The third sheet may be the same size as the first sheet in which case the third sheet is clamped to the first sheet at a disposition spaced from the ends of the first sheet or the third sheet can be longer than the first sheet and clamped at or adjacent the ends of the first sheet. In either case, the ends 28, 30 of the third sheet may be clamped by clamping means 32, 34. The length of the third sheet or the spacing of its ends 28, 30 relative to the ends of the first sheet is dependent upon the number of waves desired in the corrugation of the third sheet. This forms a curvilinear member from the third sheet in a single wave form of a substantially one-half sine wave as illustrated in FIG. 3.
Thereafter a gradual compressive force F is applied equally upon the third sheet at the crest thereof and directed toward the first sheet. This can be applied by a platen or other substantially flat beam 36 or the like applied to the top of the third sheet in a planar direction toward the first sheet. Due to the resiliency of the third sheet this force initially results in the third sheet being deformed to form a two wave curvilinear configuration as illustrated in FIG. 4. Continued application of the compressive force to the third sheet results in an increasing number of wave forms, each of which is substantially of a sine configuration. The number of curves appears to be exponentially related to the force applied to the third sheet.
When the desired number of curves are formed, or stated differently, when the desired amplitude of the crest of the third sheet relative to the first sheet is attained, the first and third sheets are bonded together at the contact point 38. The second sheet 14 may thereafter be disposed on the peaks of the third sheet remote from the first sheet and bonded thereto. Alternatively, the second sheet may be disposed on the third sheet prior to application of the compressive force intermediate the third sheet and the platen 36 and bonding of the third sheet to the first and second sheets may occur substantially simultaneously in the process. In either case when the platen is released the third sheet has been pre-stressed by an amount substantially equal to that of the compressive force and has large load bearing capacity.
A modification of the process may be utilized to form curved bodies and cylindrical members by utilizing a complimentary shaped member against which the first sheet is disposed and a platen also of that shape can be compressed toward the first sheet. For example, as illustrated in FIG. 6, to form a cylindrical body a mandrel in the form of a central member 123 having the size and shape of the inner diameter of the cylindrical body has the first sheet 112 fastened thereto. The third sheet 116, which in this case has a greater circumferential size than the first sheet, can be attached to the first sheet at its ends and a platen 136 in the form of a number of sectors 137 may be disposed about the third sheet and the sectors forcibly drawn radially inwardly to corrugate the third sheet. The second sheet can thereafter be attached to the third sheet to form the corrugated cylindrical body.
In the Prior Art invention, as illustrated in FIGS. 1-6, the sinusoidal sheet is attached at the peaks of the sine wave portions to the adjacent sheets to form a lightweight panel which may be suitable for a number of uses, including aircraft construction. However, the apparatus of the Prior Art utilized the sine wave construction and the compression of the intermediate layer only for the purposes of construction of a rigid panel.
Springs using sine-wave shaped portions are known in the art. However all of such springs utilize materials that are permanently deformed into a sine wave shape. That is to say, they are stamped, pressed, molded or otherwise shaped into a sine wave form, such that even when pressure is removed, they return to a sine wave shape. A number of patents exist which illustrate such sine wave shapes.
Syoichi, U.S. Pat. No. 5,622,358, issued Apr. 22, 1997, and incorporated herein by reference, discloses a wave spring. Syoichi discloses a wave spring formed in which a linear relation is retained between a load (P) and a deflection (S). Thereby, the degree of freedom of design of springs is enhanced. In forming a spring structure by coiling a spring material having flat cross section, a clothoid curve is selectively used as a shape-determining factor for the spring structure. This spring, however, is more of a conventional spring with a continuous spring rate.
Sylvia, U.S. Pat. No. 6,408,631, issued Jun. 25, 2002 and incorporated herein by reference, discloses a wave spring loaded split seal system. A piston includes a circumferential groove having a seal ring and spring mounted within the groove. The spring exerts an axial force on the seal ring thereby preventing motion of the seal ring within the groove. Preferably, the spring is a wave spring, wherein small changes in deflection of the wave spring produces small changes in the load generated by the spring on the seal ring. The seal ring has at least one radial spring ring mounted within the seal ring to create a radial force on the seal ring. The piston can also include a sleeve that mounts to the piston body, the sleeve forming a wall of the groove. The piston can be a displacer mounted within a cylinder of a refrigerator. This spring, also, is more of a conventional spring with a continuous spring rate.
Shibuya, European Patent No. EP0795696, issued Mar. 24, 1999 and incorporated herein by reference, discloses a coiled wave spring and production method thereof. A coiled wave spring is obtained by winding a corrugated wire into a coil shape, wherein mutually overlapping top portions and mutually overlapping base portions of the spring are in mutual contact and predetermined gaps are defined between mutually overlapping slope portions which connect the top and base portions. The first loop of the spring, that is, on the upper side, and the second loop, that is, on the lower side, are in mutual contact in an axial direction thereof only between the top portions and between the base portions, and the gaps are defined between the slope portions to prevent mutual contact. When the spring receives a load and undergoes deformation, the top portions and the base portions come into mutual contact, respectively, but hardly generate friction; Since the gaps are defined between the mutually overlapping slope portions, friction does not occur at these portions, either. This spring, also, is more of a conventional spring with a continuous spring rate.
Greenhill, U.S. Pat. No. 6,250,618, issued Jun. 26, 2001, and incorporated herein by reference, discloses a curved wave shim. A curved wave shim is formed from a flat elongated wire strip which follows a sinusoidal wave path that includes a series of waves spaced about the curved wave shim path, each wave having a shoulder portion which bears against generally parallel surfaces of the working elements positioned on a shaft or in a cylinder bore. The shim fits in a rectangular groove formed either on a shaft or in a cylinder bore, the axial height of the groove being slightly greater than the distance between successive wave crests and troughs. This spring, also, is more of a conventional spring with a continuous spring rate. Note that the sine wave shapes in this spring, as in the previously cited references, are pressed into shape and are permanent.
Price, U.S. Pat. No. 7,210,181, issued May 1, 2007 and incorporated herein by reference, discloses a spring construction. An improved spring construction for mattresses, box springs, furniture and other applications is provided. The application of such springs in mattresses, box springs, furniture and other applications is also provided. In one aspect of the invention, the spring construction is a spring including a series of spring segments, each having a flattened, irregular configuration where the spring varies in compression strength and deflection from a top portion thereof to a bottom portion thereof. Note that the sine wave shapes in this spring, as in the previously cited references, are pressed into shape and are permanent.
Fortmann, U.S. Pat. No. 4,082,375, issued Apr. 4, 1978 and incorporated herein by reference, discloses a dual wedge fluid thrust bearing including wave spring. A dual wedge thrust bearing for holding two relative rotating members in spaced relation includes a wave spring which supports both a thick flexible plate and a thin flexible plate stacked in that order between the cooperating bearing surfaces of the members. By securing the leading edge of the thin plate to the member on which the wave spring rests and in spaced relation to the cooperating bearing surface, a wedge-shaped passage is formed to create a fluid bearing which is efficient for low speeds and loads. At high speeds and loads, when the thin plate would have sagged making an inefficient wedge, the thick plate deflects against the spring at its leading edge to form a more efficient wedge-shaped opening between it and the cooperating bearing surface. Note that the sine wave shapes in this spring, as in the previously cited references, are pressed into shape and are permanent.
All of the aforementioned Prior Art patents relating to spring designs have one feature in common—while they disclose shapes that may incorporate a sine wave feature, the shapes are fixed in that they are stamped, pressed, or otherwise formed into the spring material and form part of the spring. Applicant's earlier patent discloses a sine wave corrugated material, but one that was fixed into position in the form of a bonded, corrugated sheet.